The invention relates generally to energy management systems and methods for use in connection with large, off-highway vehicles such as locomotives. In particular, the invention relates to a system and method for managing the storage and transfer of electrical energy, such as dynamic braking energy or excess prime mover power, produced by diesel-electric locomotives and other large, off-highway vehicles driven by electric traction motors.
FIG. 1A is a block diagram of an exemplary prior art locomotive 100. In particular, FIG. 1A generally reflects a typical prior art diesel-electric locomotive such as, for example, the AC6000 or the AC4400, both or which are available from General Electric Transportation Systems. As illustrated in FIG. 1A, the locomotive 100 includes a diesel engine 102 driving an alternator/rectifier 104. As is generally understood in the art, the alternator/rectifier 104 provides DC electric power to an inverter 106 which converts the AC electric power to a form suitable for use by a traction motor 108 mounted on a truck below the main engine housing. One common locomotive configuration includes one inverter/traction motor pair per axle. Such a configuration results in three inverters per truck, and six inverters and traction motors per locomotive. FIG. 1A illustrates a single inverter 106 for convenience.
Strictly speaking, an inverter converts DC power to AC power. A rectifier converts AC power to DC power. The term converter is also sometimes used to refer to inverters and rectifiers. The electrical power supplied in this manner may be referred to as prime mover power (or primary electric power) and the alternator/rectifier 104 may be referred to as a source of prime mover power. In a typical AC diesel-electric locomotive application, the AC electric power from the alternator is first rectified (converted to DC). The rectified AC is thereafter inverted (e.g., using power electronics such as Insulated Gate Bipolar Transistors (IGBTs) or thyristors operating as pulse width modulators) to provide a suitable form of AC power for the respective traction motor 108.
As is understood in the art, traction motors 108 provide the tractive power to move locomotive 100 and any other vehicles, such as load vehicles, attached to locomotive 100. Such traction motors 108 may be AC or DC electric motors. When using DC traction motors, the output of the alternator is typically rectified to provide appropriate DC power. When using AC traction motors, the alternator output is typically rectified to DC and thereafter inverted to three-phase AC before being supplied to traction motors 108.
The traction motors 108 also provide a braking force for controlling speed or for slowing locomotive 100. This is commonly referred to as dynamic braking, and is generally understood in the art. Simply stated, when a traction motor is not needed to provide motivating force, it can be reconfigured (via power switching devices) so that the motor operates as a generator. So configured, the traction motor generates electric energy which has the effect of slowing the locomotive. In prior art locomotives, such as the locomotive illustrated in FIG. 1A, the energy generated in the dynamic braking mode is typically transferred to resistance grids 110 mounted on the locomotive housing. Thus, the dynamic braking energy is converted to heat and dissipated from the system. In other words, electric energy generated in the dynamic braking mode is typically wasted.
It should be noted that, in a typical prior art DC locomotive, the dynamic braking grids are connected to the traction motors. In a typical prior art AC locomotive, however, the dynamic braking grids are connected to the DC traction bus because each traction motor is normally connected to the bus by way of an associated inverter (see FIG. 1B). FIG. 1A generally illustrates an AC locomotive with a plurality of traction motors; a single inverter is depicted for convenience.
FIG. 1B is an electrical schematic of a typical prior art AC locomotive. It is generally known in the art to employ at least two power supply systems in such locomotives. A first system comprises the prime mover power system that provides power to the traction motors. A second system provides power for so-called auxiliary electrical systems (or simply auxiliaries). In FIG. 1B, the diesel engine (see FIG. 1A) drives the prime mover power source 104 (e.g., an alternator and rectifier), as well as any auxiliary alternators (not illustrated) used to power various auxiliary electrical subsystems such as, for example, lighting, air conditioning/heating, blower drives, radiator fan drives, control battery chargers, field exciters, and the like. The auxiliary power system may also receive power from a separate axle driven generator. Auxiliary power may also be derived from the traction alternator of prime mover power source 104.
The output of prime mover power source 104 is connected to a DC bus 122 which supplies DC power to the traction motor subsystems 124A-124F. The DC bus 122 may also be referred to as a traction bus because it carries the power used by the traction motor subsystems. As explained above, a typical prior art diesel-electric locomotive includes four or six traction motors. In FIG. 1B, each traction motor subsystem comprises an inverter (e.g., inverter 106A) and a corresponding traction motor (e.g., traction motor 108A).
During braking, the power generated by the traction motors is dissipated through a dynamic braking grid subsystem 110. As illustrated in FIG. 1A, a typical prior art dynamic braking grid includes a plurality of contactors (e.g., DB1-DB5) for switching a plurality of power resistive elements between the positive and negative rails of the DC bus 122. Each vertical grouping of resistors may be referred to as a string. One or more power grid cooling blowers (e.g., BL1 and BL2) are normally used to remove heat generated in a string due to dynamic braking.
As indicated above, prior art locomotives typically waste the energy generated from dynamic braking. Attempts to make productive use of such energy have been unsatisfactory. For example, systems that attempt to recover the heat energy for later use to drive steam turbines require the ability to heat and store large amounts of water. Such systems are not suited for recovering energy to propel the locomotive itself. Another system attempts to use energy generated by a traction motor in connection with an electrolysis cell to generate hydrogen gas for use as a supplemental fuel source. Among the disadvantages of such a system are the safe storage of the hydrogen gas and the need to carry water for the electrolysis process. Still other prior art systems fail to recapture the dynamic braking energy at all, but rather selectively engage a special generator that operates when the associated vehicle travels downhill. One of the reasons such a system is unsatisfactory is because it fails to recapture existing braking energy.
Therefore, there is a need for an energy management system and method that controls when energy is captured and stored, and when such energy is regenerated for later use.
In one aspect, the invention relates to an energy management system for use with a hybrid energy diesel electric locomotive system. The locomotive system includes a locomotive having an engine. A power converter is driven by the engine and provides primary electric power. A traction bus is coupled to the power converter and carries the primary electric power. A traction drive is coupled to the traction bus. The traction drive has a motoring mode in which the traction drive is responsive to the primary electric power for propelling the locomotive on a track. The traction drive has a dynamic braking mode of operation wherein the traction drive generates dynamic braking electrical energy. The energy management system comprises an energy management processor. The energy management processor determines a power storage parameter and a power transfer parameter. An energy storage system is responsive to the energy management processor. The energy storage system selectively stores electrical energy as a function of the power storage parameter. The energy storage system selectively supplies secondary electric power from the electrical energy stored therein as a function of the power transfer parameter.
In another aspect, the invention relates to an energy management system for use with a hybrid energy off-highway vehicle. The off-highway vehicle includes a prime mover engine and a power converter driven by the prime mover engine for providing primary electric power. A traction bus is coupled to the power converter and carries the primary electric power. A traction drive is connected to the traction bus. The traction drive has a motoring mode in which the traction drive is responsive to the primary electric power for propelling the off-highway vehicle over a predetermined course. The traction drive has a dynamic braking mode of operation in which the traction drive generates dynamic braking electrical energy. The energy management system comprises an energy management processor. The energy management processor determines a power storage parameter and a power transfer parameter. An storage system is responsive to the energy management processor. The energy storage system selectively stores electrical energy as a function of the power storage parameter. The energy storage system selectively supplies secondary electric power from the electrical energy stored therein as a function of the power transfer parameter.
In still another aspect, the invention relates to an energy management method for use in connection with a hybrid energy diesel electric locomotive system. The locomotive system includes a locomotive having an engine. A power converter is driven by the engine and provides primary electric power. A traction bus is coupled to the power converter and carries the primary electric power. A traction drive is connected to the traction bus. The traction drive has a motoring mode in which the traction drive is responsive to the primary electric power for propelling the locomotive on a track. The traction drive has a dynamic braking mode of operation in which the traction drive generates dynamic braking electrical energy. The energy management method includes determining a power storage parameter and determining a power transfer parameter. Electrical energy is stored in the energy storage device as a function of the determined power storage parameter. Secondary electric power is provided from the electrical energy stored in the energy storage device as a function of the determined power transfer parameter.
In yet another aspect, the invention relates to a hybrid energy system for propelling an off-highway vehicle that is traversing a known course. The system comprises an engine. A power converter is driven by the engine and provides primary electric power. A traction motor system receives the primary electric power. The traction motor system propels the off-highway vehicle in response to the received primary electric power. The traction motor system has a dynamic braking mode of operation generating electrical energy. An energy storage system captures the electrical energy generated by the traction motor system in the dynamic braking mode, and transfers a portion of the captured electrical energy to the traction motor system to augment the primary electric power. An energy management system controls the energy storage system. The energy management system determines a power storage parameter and a power transfer parameter. The energy management system controls the capture of electrical energy by the energy storage system as a function of the energy storage parameter. The energy management system controls the transfer of the portion of the captured electrical energy by the energy storage system as a function of the power transfer parameter.
In another aspect, the invention relates to an energy management system for use in connection with a hybrid-energy off-highway vehicle that traverses a known course. The hybrid energy off-highway vehicle includes an engine. A power converter is driven by the engine and provides primary electric power. A traction motor system receives the primary electric power. The traction motor system selectively propels the off-highway vehicle in response to the received primary electric power. The traction motor system has a dynamic braking mode of operation generating dynamic braking electrical power. An energy storage system selectively stores a portion of the dynamic braking electrical power generated by the traction motor system in the dynamic braking mode. The energy storage system selectively supplies secondary electric power derived from the portion of the dynamic braking electrical power stored therein. The energy management system comprises an energy management processor. The energy management processor determines a power storage parameter and a power transfer parameter. The energy management processor controls the storage of dynamic braking electrical power by the energy storage system as a function of the power storage parameter. The energy management processor controls the supply of secondary electric power from the energy storage system as a function of the power transfer parameter.